The invention relates to an arrangement for lubricating the bearing surfaces between a tool of a hydraulic impact device and the impact device, the arrangement comprising a supply pump and at least one channel leading to the space between the bearing surfaces for supplying lubricant.
A hydraulic impact hammer comprises a tool which moves in the longitudinal direction backwards and forwards by the effect of the impact mechanism striking it. Such a tool is continuously subject to great loads; particularly when the impact hammer is moved or turned with a boom attached to a base, such as an excavator or the like suitable base, extremely great side forces may be generated in the movement range of the blade. Such forces, in turn, cause very high surface pressures for the bearing surfaces, which may damage the bearing. Further, a stroke of a percussion piston at the end of the tool causes, depending on the material to be handled, the tool to move rapidly forwards or, if the base is hard, the surface of the tool to vibrate nearly stationarily in rather an intensive manner.
Typically, the tool is implemented with either a long bearing bushing or with two separate bearing bushings at a distance from each other. A pair of bearings, i.e. bearing surfaces sliding relative to each other, is formed of the outer surface of the tool, which functions as the inner bearing surface, and correspondingly the inner surface of the bearing bushings, which functions as the outer bearing surface. In some solutions, the frame of the impact hammer is used as the outer bearing surface without separate bearing bushings. In these solutions, the materials of the bearings can vary in such a way that the tool material is usually hardened tempering steel, the bearing bushing material being carbonization-hardened steel or a bronze-based material.
Either grease or oil is used as the lubricant in the impact hammer, and the aim is to supply lubricant between the sliding surfaces to prevent a metal-metal contact and, at the same time, to even out the surface pressure between the surfaces. In particular, it has been observed that very point-like or line-like metal-metal contacts are disadvantageous and cause a great deal of wearing or, in some cases, even cracks close to the edges of the bearing surfaces. Generally, it can be said that lubrication aims at preventing the wearing of the bearing surfaces and the fastening of the metal parts to each other.
When aiming at a good lubrication result, it is particularly important to apply lubricant to such areas of the bearing surface that are known to have high surface pressures. In a hydraulic impact hammer, this refers to the upper and lower edges of the bearings in the axial direction of the bearing. This is even more important in cases where the bearing surfaces are already worn, whereby the tool may take its place more obliquely than originally relative to the centre line of the bearing.
In order to provide lubrication of the bearing and generally to ensure the lubrication, the aim has been, more and more, to replace manual lubrication used previously with automatic lubrication. In continuous automatic lubrication, there is a channel leading from the upper part of the impact hammer through its frame structure to the lower frame, and further to the bearing surfaces to be lubricated, the lubricant being supplied via the channel separately to the bearing surfaces of the tool. The lower frame, i.e. the frame part of the impact hammer around the tool, is provided with several separate branch channels to the bearing surfaces from the inlet channel of the lubricant so as to supply lubricant to different bearing surfaces. This does not, however, guarantee the supply to the intended objects of lubrication. The lubricant flow is hindered by drying of the lubricant and the resulting partial or complete clogging of the channels, the viscosity of the lubricant, great accelerations of the impact hammer during operation, the tightness of the bearings to be lubricated, the position of the impact hammer during operation, as well as dirt and moisture. In practice, it can be said that the lubricant flows along the route that is least throttled, whereby lubrication objects positioned further away as well as narrower bearing openings easily remain without lubrication when the lubricant pushes its way out through the shortest and widest route.
EP publication 0525498 discloses a solution in which the junctions of the supply channel for the lubricant and the branch channels leading to the bearings are provided with adjustable throttling elements, the aim of which is to control the flow of the lubricant. In practice, however, the problem is that although originally the lubricant could be made flow reliably to the bearing surfaces at given temperatures, for example changes in the temperature as well as dirt and drying of the lubricant will, in the long run, cause the same problems as there would be without these adjustable throttling elements.